My hair has gone thinner a bit over the past few years, but it could be for a variety of reasons. When you get older, the hairline can change. It may make you believe it's receding, but not necessarily as it is normal for hairlines to do this. Adult hairlines are different to childrens hairline and this can change over time.
At one point my hair was starting to recede, but have started using some of that Nizoral shampoo. Apparantly, it's got stuff in that stops the DHT from gripping hair roots. I've noticed it regrowing in places hair wasn't and my hairline has improved, and i've only used it for a few months. Only costs £6 and a bottle lasts a month or two if you follow the instructions on the bottle. And if you stop using it for a period, the hair doesn't shed like a motherload like that Alpecin as i've heard from @Debug Mode
Oh, and don't use Rogain/Regaine/Alpecin at all unless you really want to. These products will work, but you will be forever reliant on them to keep your hair. The day you don't use them, the day the hair sheds like crazy.